Compact HTS Ultra-Narrowband Bandpass Filter Using Novel Meander–Twin-Spiral Resonators With Interdigital Coupling Structure

A six-pole high-temperature superconducting (HTS) ultra-narrowband (UNB) bandpass filter (BPF) using novel meander-twin-spiral resonators (MTSRs) with interdigital coupling structure (ICS) is proposed in this letter. ICS can introduce an additional capacitive coupling route, thus effectively reducing the total coupling between two resonators. In addition, the total coupling can be changed by tuning the loading position of the ICS while maintaining the same spacing between two coupled resonators. For demonstration, a six-pole HTS UNB BPF at 1444MHz with a fractional bandwidth of 0.14% is designed. Good agreement between the simulated and measured results validates the proposed structure and the design method.